1. Field of the Invention
The present invention relates to a station arrangement used in a data transmission network, and particularly to an improved station arrangement to which user's equipments are connected.
2. Description of the Prior Art
FIG. 2 is a block diagram showing a prior art arrangement of stations S1 and S2. Both stations S1 and S2 have virtually the same internal structure, and in the following description their counterparts will be referred to by common symbols or by symbols with a suffix number 1 or 2 representing the stations only when their distinction is needed.
The stations S1 and S2 are linked together for data transaction with each other through a data transmission line, i.e., inter-system bus 1. Although in many cases, a large number of stations are connected to the bus 1, FIG. 2 shows only two stations for the sake of simplicity. Each station S incorporatcs a central controller CC, which is connected through a intra-system bus 2 with a desired number of terminal controllers TC, each of which is connected with a user unit T consisting of a terminal device or computer. The terminal controller TC functions to transfer user's data entered on the user unit T to the central controller CC or transfer data from the central controller CC back to the user unit T. The central controller CC has a function of network protocol for controlling the communication linkage between user units upon request, transmitting user's data packet to the destination, and confirming the data transmission, and a function of transmission line access control for implementing serial-parallel and parallel-serial conversion for the transmission of data packets and acknowledgement to another station S over a single transmission line, and arbitrating data transmission on a time-adjustment basis upon detection of data transmission conflict on a transmission line among stations.
In FIG. 2, the flow of user's data is shown by the arrows 21, 22, 23 and 26, tho flow of data packet is shown by the arrow 24, and the flow of acknowledgement of data transmission is shown by the arrow 25. Although in FIG. 2 only two stations each accompanied by only two terminal controllers TC are shown for simplicity purposes, a network usually includes more stations S on the transmission line 1 and more terminal controllers TC on each system bus 2. The system bus 2 in FIG. 2 is used to transfer data between the central controller CC and each terminal controller CC, and the two terminal controllers CC on the system bus 2 cannot transact data directly with each other.
Next, the operation of the foregoing arrangement will be described. The first example of operation is data transmission from a user unit T11 to another user unit T12, and the second example is data transmission from a user unit T11 to a user unit T22 in another station. It is assumed that the destination of user's data is already under control of the network protocol function possessed by the central controller CC.